1. Field of Invention
The present invention relates generally to the construction and use of vascular and other catheters. More particularly, the invention relates to atherectomy catheters for treating stenotic vasculature having an atheroma severing device at their distal ends.
2. Previous Art
Arteriosclerosis, also known as atherosclerosis, is a common human ailment arising from the deposition of fatty-like substances, referred to as atheroma or plaque, on the walls of blood vessels of biological conduits. Some stenotic regions also contain hard calcified deposits. Stenotic deposits occur both in peripheral blood vessels that feed the limbs of the body and coronary blood vessels which feed the heart. When deposits accumulate in localized regions of an individual's blood vessel, blood flow is restricted and that person's health is at serious risk.
Numerous approaches for reducing and removing such vascular deposits have been proposed, including balloon angioplasty, where a balloon-tipped catheter is used to dilate a region of atheroma; atherectomy, where a blade or other cutting element is used to sever and remove the atheroma; stent insertion, where a liner is placed and expanded at the site of the blockage; and laser angioplasty where laser energy is used to ablate at least a portion of the atheroma. Of particular interest to the present invention are atherectomy devices and methods where an atheroma severing device is advanced past an opening in a housing at the distal end of a vascular catheter. By positioning the housing so that a least a portion of the atheroma passes through the opening, the atheroma can be severed by advancing the atheroma severing device. Typically, such atheroma severing devices are circular cutting blades which are rotated and advanced simultaneously to effect the desired cutting.
U.S. Pat. No. 4,669,469 and European patent application EPA 163 502, each illustrate exemplary atherectomy devices of the type described above, where the cutter housing is typically a rigid metal cylinder. Rigid cutter housings, however, are problematic when the catheters are being used in small, tortuous blood vessels where the catheter tip must pass through curves having small diameters. Moreover, difficulties have been encountered in containing the circular cutting blade within the housing. It has generally been necessary to limit the area of the opening in the housing in order to assure containment and smooth travel of the blade. Such an approach is disadvantageous, however, since it limits exposure of the blade to the atheroma and the amount of atheroma which may be severed in a single pass of the blade.
To overcome the limitations inherent in rigid housing designs, the use of flexible cutter housings has been proposed. U.S. Pat. No. 4,781,186, describing the construction of atherectomy catheters having flexible cutter housings which may comprise a slotted metal or metal braid configuration. While the use of flexible housings provides an improvement in the ability to position the distal end of the catheter within tortuous portions of the vascular system, such flexible housings exacerbate the problems with guiding the atheroma severing device within the housing. The ability to traverse the more tortuous blood vessels is related to the length of the inflexible section of the device, or the length of the least flexible portion of the cutter. What is needed is an atherectomy device that can at once be navigated through tortuous portions of the vascular system and provide for smooth guidance of the atheroma severing device within its housing.